In construction, floor and roofs are often constructed with metal decking which may enclose insulation. The decking is provided with ribs; usually ribs with symmetrical yet non-parallel side walls. Because of the rib configuration, the decking is termed a trapezium. The decking will usually form the unfinished ceiling of the space below. It is necessary and common to hang utilities such as plumbing, wiring, air ducts, and other items such as a finished ceiling from the trapezium.
Hangers for such purposes usually engage a hole or tang punched from the non-parallel side walls or bottom of such ribs. The hanger may then simply be hooked into or on the hole or tang. However, load capacity is poor.
One type of hanger employed with good load capacity is similar to a clevis. Holes are punched in the side walls of the trapezium and a U-shape hanger is supported by an elongated bolt inserted through such holes and holes in the upper ends of the legs of the hanger. The legs of the hanger straddle the trapezium rib. The hanger is held in place, for example, by a head on one end of a bolt and a nut and washer on the other end, or a threaded rod with two nuts. The bight portion of the hanger is provided with a hole, thread form, nut, key slot, or other similar device for affixing something to be hung from the bottom of the hanger, using for example, plain or threaded rod, wire, or other forms of clips or clamps.
Some of the problems of such a hanger are its cost, its multiple parts, and its difficulty of installation. Such hangers have a minimum of three parts and may have five or more, depending on whether a separate fixing device or washer is employed. Since the installation is usually done on a scaffold or step ladder, loose parts can be a problem. Even if all of the parts as a set are packaged, the opening of the package and assembly of the parts can be a problem. If one of the parts drops or rolls away, the installer has to climb down to retrieve the part, if it can be found, or get another package. Multiple part fasteners always take more time to install, and are more costly, especially if packaged.
It would accordingly be desirable to have the advantages of a clevis type hanger without the multiple parts or added cost.